The solution to the problem that mt Manager can't sign again is as follows:

1. Try to use the latest version of MT Manager. An updated version may have fixed the problem.

2. Make sure that the mobile phone is root, otherwise the MT manager can't make a second signature.

3. Try using other similar tools, such as RootExplorer and ES file browser.

4. If the mobile phone is already root, you can try to solve this problem by modifying the file permissions. The specific method is: open MT Manager, find the file to be operated, press and hold the file and select "Properties", set the permission of the file to "0755" in the pop-up window, and then sign again after saving.